Rudders are used in variety of vessels, such as many types and classes of ships, for controlling and manipulating the direction of the vessels. Typically, the rudder extends below or behind the hull of the vessel. The direction of the vessel is controlled by rotating or turning the rudder. Turning and holding a vessel's rudder may be referred to as rudder actuation.
A variety of hydraulic mechanisms exist for rudder actuation including rapson slides, link types, articulated cylinders, rotary vanes, and hydraulic rotaries. In general, the hydraulic mechanisms are mounted directly to a vertical shaft of the rudder, referred to as a rudder stock, or indirectly through one or more tillers. For example in a rotary vane 10 as shown in FIG. 1, a number of vanes 12 are coupled to the rudder stock 14 such that the turning of the vanes 12 by the application of hydraulic pressure turns the rudder stock 14. As another example in a rapson slide 20 as shown in FIG. 2, a pair of opposing hydraulic cylinders 22, 24 are coupled to a tiller 26 for moving the tiller 26 back and forth such that tiller 26 turns the rudder stock. Other hydraulic mechanisms may include a rack driven by one or more hydraulic cylinders or pumps and a pinion coupled directly to the rudder stock.
Although hydraulic mechanisms are capable of producing the large forces required for rudder actuation, hydraulic mechanisms also have disadvantages and shortcomings. For example, the hydraulic fluids inherent to such mechanisms are potential environmental and safety liabilities. Many of the hydraulic mechanisms are relatively heavy and noisy. Moreover, most hydraulic mechanisms are maintenance intensive and often require the vessel to carry additional crew members for maintaining the hydraulic mechanisms. Another issue with hydraulic mechanisms, especially ones directly coupled to the rudder stock, is the overall steering system's resistance to shock. More specifically, a variety of sources, such as a grounding or an underwater explosion, may cause the rudder stock to move up and down relative to the ship's hull. The vertical movement of the rudder stock may be referred to as a rudder stock excursion. The direct coupling of the hydraulic or another other type of drive mechanisms to the rudder stock creates a problem during a rudder stock excursion because the movement of the rudder stock directly transfers stress loads onto components of the drive mechanisms. The problem is especially acute in many of the hydraulic mechanisms that require relative tight tolerances. In such mechanisms a relatively small displacement between components can severally degrade the performance of the steering system or lead to more lengthy and expensive maintenance. To protect against rudder stock excursions some known hydraulic mechanisms use components that are especially hardened or processed to better withstand some of the stress loads. However, such components increase the overall cost, weight, size, and complexity of the hydraulic mechanism and the steering system as a whole.
In light of the foregoing it would be desirable to provide a steering mechanism for a vessel that is not driven by hydraulics. Also, it would be desirable if the steering mechanism was easier to assemble and maintain than many of the known hydraulic mechanisms. Other desirable characteristics may include relatively lighter, quieter, and improved shock resistance compared to at least some of the known hydraulic systems.